1. Field of the Invention
The present invention relates to a bar which has magnetic poles at selected side portion thereof, and also relates to a method and an instrument for manufacturing the magnet.
2. Description of the Prior Art
When a ruminant, a cow in particular, eats feed, it often eats by mistake metallic foreign bodies, such as wire, nails, etc. having sharp edges, admixed, with the feed. It swallows such metallic foreign bodies without masticating the same due to its own behavior. The metallic foreign bodies are substantially identified with iron scraps and collected in the reticulum of cattle by the movement of the paunch thereof. The reticulum serves not only to effect a chemical action but also to repeat vigorous contraction and relaxation for the purpose of mechanically mixing the feed. For this reason, the metallic foreign bodies laid on the bottom of the reticulum often pierce through or perforate the walls thereof due to the aforementioned vigorous contraction to thereby injure important adjacent organs, such as the diaphragm, pericardium, myocardium, liver, spleen, etc. Such afflictions as this injury cause a number of cattle to go out of use, and inflict dire damage upon the owners.
In order to prevent such injuries due to the presence of metallic foreign bodies as described above from occurring, there has heretofore been adopted oral administration of a bar magnet, such as that having grooves formed in the outer circumference thereof in the lengthwise direction, for example, into the reticulum of cattle. This bar magnet can catch by magnetic attraction the metallic foreign bodies thereon to reduce the injuries to some extent.
However, since a conventional permanent magnet has the north and south poles on the opposite ends thereof, enjoys high remanence in intensity only at the opposite ends, exhibits sudden reduction in magnetic attraction toward the center thereof, and possesses little desired remanence at the intermediate portion thereof, the metallic foreign bodies caught on the surface of the magnet within the reticulum of a ruminant project from the opposite ends of the magnet. As a result, the magnet comes to gain in length and have sharp leading ends, and allows the sharp leading ends to be liable to pierce through the walls of the reticulum.
If a magnet has magnetic poles at the intermediate portion thereof in the lengthwise direction, even when it catches metallic foreign bodies on the opposite ends thereof in a state wherein the metallic foreign bodies protrude from the opposite ends of the magnet, only a slight force exerted thereon causes the substances to be slid on the sides of the magnet and adhered intimately to the side walls of the magnet in the lengthwise direction, thereby making it possible for the magnet to function effectively, to have a large magnetic attraction and to prevent the adverse injuries from occurring. Thus, there is now an increased demand for magnets having strong attractive force at the intermediate portion thereof.